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The Single UNIX &reg; Specification, Version 2<br>
Copyright &copy; 1997 The Open Group

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<h4><a name = "tag_000_001_077">&nbsp;</a>NAME</h4><blockquote>
acos - arc cosine function
</blockquote><h4><a name = "tag_000_001_078">&nbsp;</a>SYNOPSIS</h4><blockquote>
<pre><code>

#include &lt;<a href="math.h.html">math.h</a>&gt;

double acos(double <i>x</i>);
</code>
</pre>
</blockquote><h4><a name = "tag_000_001_079">&nbsp;</a>DESCRIPTION</h4><blockquote>
The
<i>acos()</i>
function computes the principal value of the arc cosine of
<i>x.</i>
The value of
<i>x</i>
should be in the range [-1,1].
<p>
An application wishing to check for error situations should set
<i>errno</i>
to 0 before calling
<i>acos()</i>.
If
<i>errno</i>
is non-zero on return, or the value NaN is returned,
an error has occurred.
</blockquote><h4><a name = "tag_000_001_080">&nbsp;</a>RETURN VALUE</h4><blockquote>
Upon successful completion,
<i>acos()</i>
returns the arc cosine of
<i>x,</i>
in the range [0,&nbsp;<sub><img src="../images/pi.gif" border=0></sub>] radians.
If the value of
<i>x</i>
is not in the range [-1,1],
and is not &plusmn;Inf or NaN, either 0.0 or NaN is returned
and
<i>errno</i>
is set to [EDOM].
<p>
If
<i>x</i>
is NaN, NaN is returned and
<i>errno</i>
may be set to [EDOM].
If
<i>x</i>
is &plusmn;Inf, either 0.0 is returned and
<i>errno</i>
is set to [EDOM], or NaN is returned and
<i>errno</i>
may be set to [EDOM].
</blockquote><h4><a name = "tag_000_001_081">&nbsp;</a>ERRORS</h4><blockquote>
The
<i>acos()</i>
function will fail if:
<dl compact>

<dt>[EDOM]<dd>
The value
<i>x</i>
is not &plusmn;Inf or NaN and
is not in the range [-1,1].

</dl>
<p>
The
<i>acos()</i>
function may fail if:
<dl compact>

<dt>[EDOM]<dd>The value
<i>x</i>
is &plusmn;Inf or NaN.

</dl>
<p>
No other errors will occur.
</blockquote><h4><a name = "tag_000_001_082">&nbsp;</a>EXAMPLES</h4><blockquote>
None.
</blockquote><h4><a name = "tag_000_001_083">&nbsp;</a>APPLICATION USAGE</h4><blockquote>
None.
</blockquote><h4><a name = "tag_000_001_084">&nbsp;</a>FUTURE DIRECTIONS</h4><blockquote>
None.
</blockquote><h4><a name = "tag_000_001_085">&nbsp;</a>SEE ALSO</h4><blockquote>
<i><a href="cos.html">cos()</a></i>,
<i><a href="isnan.html">isnan()</a></i>,
<i><a href="math.h.html">&lt;math.h&gt;</a></i>.
</blockquote><h4>DERIVATION</h4><blockquote>
Derived from Issue 1 of the SVID.
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UNIX &reg; is a registered Trademark of The Open Group.<br>
Copyright &copy; 1997 The Open Group
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